FBA fees for NBA 2K16 are about $11 so your takehome is about $43 if you assume a price of $55. FBA fees for the XBox are about $33 at a price of $400 so your takehome is about $365. This is before shipping which may cost $5-$10 between the two of them depending on how many you buy at once. Let's call it $10 for shipping.

If the prices hold stead and you earn $405-$410 for both sales after fees, that's a profit margin of $35 for the sale or 9.5%

So here's the bonus cash:

Start with Inbox Dollars = $18.5.
2% in eBay Bucks = $7.40
Use up eBay Gift Cards or eBay Bucks- You can either use eBay gift cards which hopefully you bought at a discount or you can use a credit card that earns 2% which would be another $7.40

Overall, you could earn over $65 per XBox, over 17% and even better if you use eBay gift cards. I will buy these as a way to liberate my eBay Bucks.

Keep in mind that there is a maximum use of $5,000 of eBay Gift Cards per rolling 180 days. Also, sometimes there is a maximum of 5, 7, 8 or 9 eBay Gift Cards that you can use in one transaction before the transaction times out.

Here is where it gets a little hairy: there is another listing on Amazon that combines the two - the XBox and the game. If I had to guess I think that the XBox can be sold separately from the game, but I can't say with absolute conviction. Please be aware of this. If you can only sell for $400, you lose all your profit from the sale, but you get to keep the extras so it still isn't so bad.